1. Field of the Invention
This invention relates to diesel type pile driving hammers and in particular it concerns novel methods and apparatus for starting such hammers.
2. Description of the Prior Art
Diesel type pile driving hammers are well known in the construction industry. One example is the Model 520 Diesel Pile Hammer supplied by International Construction Equipment, Inc., 301 Warehouse Drive, Matthews, N.C.
In a typical diesel hammer, a heavy ram falls in a cylinder onto an anvil mounted on the top of a pile. The impact of the ram on the anvil drives the pile down. During the fall of the ram, the air under the ram is compressed into one or more pockets formed in the upper surface of the anvil. At the time the ram strikes the anvil, fuel is admitted to the anvil pockets and mixes with the compressed air and explodes to drive the ram back up inside the cylinder for another stroke. During the rise and subsequent fall of the ram, it passes by exhaust and inlet ports in the cylinder to allow discharge of the products of combustion and admission of fresh air to be compressed. Thus, once the hammer begins operation it continues to operate in an automatic manner.
Various techniques have been proposed to start the operation of diesel type hammers. The most common technique for starting a diesel hammer, involves lifting the ram inside the casing with a rope and then releasing the ram so that it falls down through the cylinder with sufficient force to compress the air trapped in the cylinder between the ram and the anvil. Then, when fuel is injected into the cylinder it will explode to drive the ram upwardly. Other techniques which have been proposed for starting the operation of a diesel hammer involve the use of a hydraulic piston and cylinder assembly mounted alongside the hammer casing. The piston rod is connected, via a releasable latch which extends through a slot in the casing, to a ledge or lip formed in the ram. When the piston and cylinder assembly is energized the piston pulls the piston rod, latch and ram upwardly. When the ram reaches a predetermined height, the latch is tripped, allowing the ram to fall.
The known prior art diesel hammer starting techniques and mechanisms are relatively complicated and are subject to malfunction. Also they require the formation of elongated slots along the hammer casing which constitutes a potential weakness in its construction.
It as also known, as described in copending U.S. patent application Ser. No. 405,615, filed Aug. 5, 1982 and assigned to the assignee of the present invention, to use a compressed gas to drive the ram of a diesel hammer up against an upper anvil so that the hammer can be used for upward pulling as well as for downward driving. The compressed gas techniques as described in that patent application, however, is not used for starting the diesel operation. In fact, in its operation the diesel hammer air inlet and exhaust ports are closed and the compressed gas, in addition to driving the ram upwardly, also cushions the downward fall of the ram so that it does not drive downwardly on the anvil.